This invention relates generally to power line testing equipment and particularly to a power circuit locater for identifying which of a number of circuit interrupter devices is in the circuit that supplies a particular power outlet.
A common problem encountered by professional electricians (and home handymen) is that of identifying the circuit breaker or fuse in a building electrical power panel that is in the circuit that supplies power to a particular electrical power outlet receptacle, hereinafter referred to simply as an outlet. In certain environments, such as hospitals, it is important that the electrician not inadvertently interrupt power flow to a critical area in attempting to determine which of the many fuses or circuit breakers in the electrical power panel is associated with the specific outlet that is to be worked on.
There is a tester currently available for determining the fuse or circuit breaker that is in the power supply circuit for a particular outlet. The tester is quite expensive, selling for hundreds of dollars, and includes a transmitter that incorporates a high voltage transistor, a diode and a resistor, and a crystal oscillator. The transmitter is connected across the AC line (to the outlet) and develops an oscillatory signal of about 4.5 kHz. Basically it connects and disconnects a resistor across the AC line at a 4.6 kHz rate. The resistor is rated at about 10 watts and the tester draws about 100 ma of current. The system requires a very sensitive receiver to pick up the magnetic field from the very low amplitude 4.6 kHz signal current that flows to the outlet from the electrical panel via the house wiring. The receiver includes an analog to digital converter and a plurality of light emitting diodes (LEDs) which are progressively illuminated to indicate the intensity of the received signal. Further details of the circuit arrangements in this tester are not known. It is clear though that sophisticated circuitry is required in the receiver to reject the strong 60 Hz power signal.
The circuit arrangement of the invention, on the contrary, is of simple construction and has significantly lower cost. Its principle of operation is, however, substantially the same. A passive signal device is plugged into the outlet in question and an identification signal current is drawn over the circuit house wiring from the electrical panel or fuse box. The identification signal current that is drawn from the power source by the passive signal device is detected by a suitable receiver. In accordance with the invention, the identification signal is a single pulse having a very large amplitude and an extremely short duration (2.0 microseconds in the preferred embodiment). A repetition rate of about 7.0 Hz for the identification signal is selected to produce a distinct visual, and/or audio indication that is readily distinguishable from any other signals that may be present on the house wiring circuit. Because of the large amplitude of the identification signal current drawn from the AC power source, a broadly tuned and relatively insensitive receiver may be used. The necessity for complex and expensive 60 Hz rejection circuitry is therefore completely obviated. The result is a very simple, economical and accurate arrangement for determining the circuit breaker or fuse in an electrical power panel that supplies power to a particular outlet.